In the Bluetooth System Preferences panel, if you option-click on a device in the left-hand side of the window, you'll see more detailed information about that device on the right-hand side of the window. This is the same information you'll see if you select the device, click the Action (gear) icon at the bottom of the window, and choose Show More Info from the pop-up menu.

Also, if you open the Bluetooth System Preferences pane while holding down the Option key, it will default to the Show More Info display for the last-selected device.

[robg adds: Holding down the Option key is much simpler than using the contextual menu. This works in at least 10.5 and 10.6; I'm not sure about 10.4.]